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Xue Qin,
Hui Lv,
Zengnan Mo,
Zhiping Chen,
Liwen Lin,
Tao Peng,
Haiying Zhang,
Xiaobo Yang,
Yong Gao,
Aihua Tan,
Shan Huang,
Haiwei Li,
Huiling Wu, Yan Deng,
Shan Li
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ABSTRACT: The aim was to establish reference intervals for serum sex hormones in adult men in the Fangchenggang area of China.
Serum samples from 1,191 healthy male subjects, aged 20 - 69 years, were collected from the Fangchenggang Area Male Health and Examination Survey (FAMHES). Total testosterone (T), estrogen (E2), luteinising hormone (LH), follicle-stimulating hormone (FSH), and sex hormone-binding globulin (SHBG) were measured by electrochemiluminescence immunoassay (Elecsys). Free testosterone (FTc) was calculated from the concentrations of T, SHBG, and albumin.
The total nonparametric reference intervals for male sex hormones in our study were 12.6 - 37.0 nmol/L for T, 0.24 - 0.69 nmol/L for FTc, 65.4 - 207.7 pmol/L for E2, 2.2 - 11.6 IU/L for LH, 1.8 - 16.5 IU/L for FSH, and 18.2 - 95.1 nmol/L for SHBG. Age had a significant positive association with LH (r = 0.218), FSH (r = 0.427), and SHBG (r = 0.427) and a negative association with FTc (r = -0.383) and E2 (r = -0.098), but no significant association with T after adjustment for BMI. The age-dependent reference intervals were also calculated. Higher T and FTc concentrations were found in men who smoke compared with non-smokers, while no significant differences were found in E2, LH, FSH, and SHBG. When stratified for the number of cigarettes smoked per day, we found that the distributions of serum T levels were significantly higher only in the smokers who smoked 11 or more cigarettes a day than the non-smokers. Unlike T, the distributions of serum FTc levels were significantly higher only in the smokers who smoked less than 11 cigarettes a day, while the FSH levels were significantly lower.
In clinical practice, single reference intervals can be used for men aged 20 - 69 years for T and E2 measured with the Elecsys method, but separate age-dependent reference intervals should be used for FTc, LH, FSH, and SHBG. In addition, distinct reference intervals for T should be established for non-smokers or smokers (1 - 10 cigarettes/day) and smokers (> or = 11 cigarettes/day).
Clinical laboratory 01/2012; 58(3-4):281-90. · 0.90 Impact Factor
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ABSTRACT: A study is made of the role of flaw state on the strength properties of brittle ceramic coating layers bonded to soft polycarbonate substrates. We introduce Vickers radial cracks at prescribed loads into the coating undersurfaces prior to bonding to control the sizes and locations of the starting flaws. A spherical indenter is then loaded on the top bilayer surfaces, directly above the Vickers indentation sites, subjecting the radial cracks to flexural tensile stress. Radial crack responses are monitored in situ, using a camera located below the transparent substrate. Critical loads to cause radial crack instability, and ensuing growth of the arrested cracks, are recorded. Conventional biaxial flexure tests on corresponding monolith coating materials provide a baseline for data comparison. Relative to the monolith flexure specimens, the bilayers show higher strengths, the more so the larger the flaw, indicating enhanced flaw tolerance. A simple fracture mechanics analysis of the radial crack evolution in the concentrated-load field, with due account for distribution of flexural tensile stresses at the coating undersurface, is unable to account completely for the enhanced bilayer strengths for the larger Vickers flaws. It is hypothesized that the epoxy used to bond the bilayer components enters the cracks, causing crack-wall adherence and providing an increased resistance to radial crack instability. The fracture mechanics are nevertheless able to account for the arrest and subsequent stable extension of the radial cracks beyond the critical loads once this extraneous adherence has been overcome.
Journal of the American Ceramic Society 12/2004; 84(10):2377 - 2384. · 2.27 Impact Factor
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ABSTRACT: Results from a systematic study of damage in material structures representing the basic elements of dental crowns are reported. Tests are made on model flat-layer specimens fabricated from various dental ceramic combinations bonded to dentin-like polymer substrates, in bilayer (ceramic/polymer) and trilayer (ceramic/ceramic/polymer) configurations. The specimens are loaded at their top surfaces with spherical indenters, in simulation of occlusal function. The onset of fracture is observed in situ using a video camera system mounted beneath the transparent polymer substrate. Critical loads to induce fracture and deformation at the ceramic top and bottom surfaces are measured as functions of layer thickness and contact duration. Radial cracking at the ceramic undersurface occurs at relatively low loads, especially in thinner layers. Fracture mechanics relations are used to confirm the experimental data trends, and to provide explicit dependencies of critical loads in terms of key variables: material-elastic modulus, hardness, strength and toughness; geometric-layer thicknesses and contact radius. Tougher, harder and (especially) stronger materials show superior damage resistance. Critical loads depend strongly (quadratically) on crown net thickness. The analytic relations provide a sound basis for the materials design of next-generation dental crowns.
Biomaterials 07/2004; 25(14):2885-92. · 7.40 Impact Factor
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ABSTRACT: Fracture damage in trilayers consisting of outer and inner brittle layers bonded to a compliant (polycarbonate) substrate and subjected to concentrated surface loading is analyzed. The principal mode of fracture is radial cracking at the undersurface of the inner (core) layer, even in the strongest of core ceramics--other damage modes, including radial cracking in the outer (veneer) layer, are less invasive in these all-brittle coating systems. Tests on simple trilayer structures fabricated from glasses, sapphire, and dental ceramics are used to examine the dependence of the critical load for radial fracture in terms of relative outer/inner layer thickness and modulus, and inner layer strength. An explicit relation for the critical load, based on a flexing plate model in which the outer/inner bilayer is reduced to an "equivalent" monolithic coating with "effective" composite modulus, is used to examine these dependencies. The theoretical relation describes all the major trends in the critical load data over a broad range of variables, thus providing a sound basis for trilayer design. Relevance of the analysis to dental crowns and other biomechanical applications is a central theme of the study.
Journal of Biomedical Materials Research Part A 01/2004; 67(3):828-33. · 2.63 Impact Factor
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ABSTRACT: In this article, we review recent advances in the understanding and analysis of damage initiation and evolution in laminate structures with brittle outerlayers and compliant sublayers in concentrated loading. The relevance of such damage to lifetime-limiting failures of engineering and biomechanical layer systems is emphasized. We describe the results of contact studies on monolayer, bilayer, trilayer, and multilayer test specimens that enable simple elucidation of fundamental damage mechanics and yet simulate essential function in a wide range of practical structures. Damage processes are observed using post mortem (“bonded-interface”) sectioning and direct in situ viewing during loading. The observations reveal a competition between damage modes in the brittle outerlayers—cone cracks or quasiplasticity at the top (near-contact) surfaces and laterally extending radial cracks at the lower surfaces. In metal or polymeric support layers, yield or viscoelasticity can become limiting factors. Analytical relations for the critical loads to initiate each damage mode are presented in terms of key system variables: geometrical (layer thickness and indenter radius); material (elastic modulus, strength and toughness of brittle components, hardness of deformable components). Such relations provide a sound physical basis for the design of brittle layer systems with optimal damage thresholds. Other elements of the damage process—damage evolution to failure, crack kinetics (and fatigue), flaw statistics, and complex (tangential) loading—are also considered.
Journal of Materials Research. 11/2002; 17(12):3019 - 3036.
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ABSTRACT: Results of contact tests using spherical indenters on flat ceramic coating layers bonded to compliant substrates are reported for selected dental ceramics. Critical loads to produce various damage modes, cone cracking, and quasiplasticity at the top surfaces and radial cracking at the lower (inner) surfaces are measured as a function of ceramic-layer thickness. It is proposed that these damage modes, especially radial cracking, are directly relevant to the failure of all-ceramic dental crowns. The critical load data are analyzed with the use of explicit fracture-mechanics relations, expressible in terms of routinely measurable material parameters (elastic modulus, strength, toughness, hardness) and essential geometrical variables (layer thickness, contact radius). The utility of such analyses in the design of ceramic/substrate bilayer systems for optimal resistance to lifetime-threatening damage is discussed.
Journal of Biomedical Materials Research 02/2002; 63(2):137-45.
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ABSTRACT: Simple relations for the onset of competing brittle and quasi-plastic damage modes in Hertzian contact are presented. The formulations are expressed in terms of well-documented material parameters, elastic modulus, toughness, and hardness, enabling a priori predictions for given ceramics and indenter radii. Data from a range of selected ceramic (and other) materials are used to demonstrate the applicability of the critical load relations, and to evaluate coefficients in these relations. The results confirm that quasi plasticity is highly competitive with fracture in ceramics, over a sphere radius range 1–10 mm. Implications concerning the brittleness of ceramics in the context of indentation size effects are discussed.
Journal of the American Ceramic Society 02/2001; 84(3):561 - 565. · 2.27 Impact Factor
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ABSTRACT: A FEA study of coating/substrate bilayers is conducted as a foundation for damage analysis. Attention is focused on the stresses along the contact axis immediately adjacent to the bilayer interface, where radial cracking or yield in the coating, or yield in the substrate, tend to occur. The stress analysis is used to determine critical loads to initiate each damage mode in terms of basic material properties and coating thickness. Controlling material parameters are strength (brittle mode) and yield stress or hardness (plastic mode). The critical loads are shown to have a simple quadratic dependency on coating thickness, but more complex dependencies on elastic modulus mismatch ratio. Simplified explicit modulus functions afford a route to prediction of the critical loads for design purposes. Implications concerning the design of bilayers for specific applications are discussed.
Acta Materialia.
